Numerous different cardiac arrhythmias are treated through implantable devices. Arrhythmias that can be treated with such devices include atrial and ventricular fibrillation, as well as less pronounced arrhythmias. Since such devices typically contain their own power supply, it is desireable to accurately predict when a therapeutic electrical pulse should be administered so that unnecessary pulses can be avoided. It is also desireable to be able to predict arrythmias in advance of onset or at an early phase, before the arrythmia progresses to a serious stage such as ventricular fibrillation. Accordingly, almost all implantable arrhythmia treatment devices incorporate sensing electrodes and sensing circuitry.
Current sensing electrodes are positioned on the right side of the heart, at the end of the defibrillation lead. Such sensing electrodes collect little information on electrical activity in the left ventricle. Because most arrhythmias originate in the left ventricle, obtaining left ventricle electrical information is highly desireable to providing an indication of risk of arrhythmia. In addition, spatial distribution of sensing electrodes (i.e., separating the electrodes in different locations) is also important, because spatially separate electrodes gather information from a greater volume of heart tissue. But, it is undesireable to place an electrode in the left ventricle because of the risk of clott formation on the catheter, leading to stroke.
In view of the foregoing, there is a continued need for new sensing electrode configurations and techniques that can be employed in implantable arrhythmia treatment apparatus.